1. Field of the Invention
The present invention relates to a semiconductor device suited to the formation of a wiring layer, and a method of fabricating the semiconductor device.
2. Description of the Related Art
Recently, a method using a three-layered hard mask is used when a wiring layer is to be formed by using the damascene method. FIGS. 8A to 8D are sectional views showing a conventional semiconductor device fabrication method using the damascene method in order of steps.
In this conventional fabrication method, as shown in FIG. 8A, a Cu film 102 is buried in an interlayer dielectric film 101. On these films, an SiC film 103 as a barrier film, a porous silica film 104, an SiC film 105 as a cap film, an SiO2 film 106, an SiN film 107, and an antireflection film 108 such as a BARC (Bottom Anti Reflection Coating) are formed in this order. In addition, a resist mask 109 made of an ArF resist is formed.
Subsequently, as shown in FIG. 8B, the resist mask 109 is used as a mask to etch the antireflection film 108 and SiN film 107. Then, the resist mask 109 and antireflection film 108 are removed by ashing. After that, the SiN film 107 is used as a mask to etch the SiO2 film 106. The SiO2 film 106 is then used as a mask to etch the SiC film 105 and remove the SiN film 107.
As shown in FIG. 8C, the SiO2 film 106 is used as a mask to etch the porous silica film 104.
As shown in FIG. 8D, the SiO2 film 106 is used as a mask to etch the SiC film 103. After that, an interconnection is formed.
Conventionally, Cu interconnections are formed by the damascene method as described above, and fine low-resistance interconnections are obtained.
Unfortunately, in the above-mentioned damascene method, as shown in FIG. 8D, when the SiC film 103 as a barrier film is etched, the porous silica film 104 as a low-dielectric-constant film is processed by side etching. Consequently, the side portions of the porous silica film 104 recede. This phenomenon appears not only for a porous silica film but also for other inorganic low-dielectric-constant films, e.g., an SiOC film, SiOCN film, porous SiOC film, and porous SiOCN film.
Prior Arts are disclosed in Patent reference 1 (Japanese Patent Application Laid-Open No. 2003-124189), Patent reference 2 (Japanese Patent No. 3250518), Patent reference 3 (Japanese Patent No. 3365554), and Patent reference 4 (Japanese Patent Application Laid-Open No. 2002-26121).